Advice on D300 repair

Hopefully this won't be a repost/double post, though predictable for a forum newbie...I waited the couple of minutes (actually more than 15) for this caching issue described on the new post edit page, but after my first attempt at posting but my new thread doesn't appeared to have shown up at all...

Have a fairly light use D300 (under 4k total image count) owned since new that developed a severe problem that I suspect is related to a faulty circuit board or perhaps firmware gone bad, if there is such a thing. Camera sat in a dry, relatively cool location for about 6-8 months since last time it was used. Went to use it about 2 months ago, noticed the audible beeps were missing, then saw right away the dynamic AF mode was now MIA. Center focus and average(?) focus are very slow to function and often "gets confused" when doing its thing. Not sure if there are other problems as well, but most everything else I've tried seems to operate correctly.

Not sure where the manuals have been stored (
Instructions? Guys don't need instructions...
), so I figured I'd find a knowledgeable website to ask for advice.

Can the camera's firmware be re-flashed by me?

If I do have to send it to a repair shop, are some authorized repair shops better and/or more preferred than others? Never really had to deal with dSLR repair until now, so I definitely am looking for sage advice in this regard. Up until now, all of my film Nikon needs had been addressed locally, but according to Nikon USA's website there are not factory certified repair centers nearby for the D300.